Induction of a relatively fast transbilayer movement of phosphatidylcholine in vesicles. A 13CNMR study

[N-13CH3]Phosphatidylcholines are introduced into the outer monolayer of phosphatidylcholine vesicles with the phosphatidylcholine exchange protein from bovine liver. The transbilayer distribution of the [N-13CH3]phosphatidyl-choline is measured with 13C NMR. The transbilayer movements of [N-13CH3]-dioleoyl phosphatidylcholine and [N-13CH3]dimyristoyl phosphatidylcholine at 30 degrees C in vesicles composed of these phosphatidylcholines are extremely slow processes with estimated half-times of days. [N-13CH3]Dioleoyl phosphatidyl-choline introduced into dimyristoyl phosphatidylcholine vesicles migrates from the outer to the inner monolayer with a half-time of less than 12 h. The data suggest that differential changes in the lateral packing of the two monolayers might be a driving force for transbilayer transport of phospholipids.